The invention relates to a process for reducing the agglomeration tendency of hydrates of natural gases, petroleum gases or other gases by the use of at least one additive. The gases which form hydrates can in particular incorporate at least one hydrocarbon chosen from among methane, ethane, ethylene, propane, propene, n-butane and isobutane and optionally H.sub.2 S and/or CO.sub.2.
These hydrates form when water is present with the gas, either in the free state, or dissolved in a liquid phase, such as a liquid hydrocarbon, and when the temperature reached by the mixture, particularly of water, gases and optionally liquid hydrocarbons, such as oil, drops below the thermodynamic temperature for the formation of hydrates, said temperature being given for a known gas composition and when the gas pressure is fixed.
Hydrate formation is feared, particularly in the oil and gas industries, where the conditions for the formation of hydrates frequently occur. Thus, in order to reduce the production costs of crude and gas, both with respect to the capital costs and with regards to the operating costs, one way considered, particularly in the case of ocean production, is to reduce or eliminate the treatments applied to the crude or gas to be transported from the field to the coast and to leave all or part of the water in the fluid to be transported. These ocean treatments generally take place on a platform located on the surface in the vicinity of the field, so that the initially hot effluent can be treated prior to the reaching of the thermodynamic conditions for the formation of hydrates as a result of the cooling of the effluent by the ocean water.
However, as occurs in practice, when the thermodynamic conditions necessary for the formation of hydrates are combined, the agglomeration of the hydrates leads to the filling and blocking of the transportation pipes by the creation of plugs, which prevent any passage of gas or crude oil.
The formation of hydrate plugs can lead to a production stoppage and therefore cause considerable financial losses. Moreover, putting back into service of the installation, particularly in the case of ocean transportation or production, can take a long time, because it is very difficult to decompose the hydrates formed. Thus, when the production of an underwater field of natural gas or oil and gas containing water reaches the surface and is then transported to the ocean bed, as a result of the lowering of the temperature of the effluent produced, thermodynamic conditions are combined so that hydrates form, agglomerate and block the transfer pipes. The temperature at the ocean bed can e.g. be 3.degree. or 4.degree. C.
Favorable hydrate formation conditions can also occur in the same way on land, in the case of pipes which are either not buried or not buried sufficiently deeply, e.g. when the ambient air temperature is low.
In order to obviate these disadvantages, the prior art has sought to use products which, added to the fluid, could act as inhibitors by lowering the thermodynamic hydrate formation temperature. They are in particular alcohols, such as methanol, or glycols, such as mono-, di-or tri-ethylene glycol. This solution is very onerous, because the inhibitor quantity to be added can reach 10 to 50% of the water content and these inhibitors are difficult to recover in a complete manner.
It has also been recommended that the transportation pipes be insulated in such a way as to prevent the temperature of the transported fluid from reaching the hydrate formation temperature under operating conditions. However, such a procedure is also very expensive.
In addition, various anionic or nonionic surfactants have been tested for their effect in delaying the formation of hydrates within a fluid containing a gas, particularly a hydrocarbon, and water. Reference can e.g. be made to the article by Kuliev et al "Surfactants studied as hydrate-formation inhibitors" Gazovoe Delo No. 10, 1972, pp. 17 to 19, reported in Chemical Abstracts 80, 1974, 98122r.
A description has also been given of the use of additives able to modify the hydrate formation mechanism, because instead of rapidly agglomerating with one another and forming very solid plugs, the hydrates formed disperse in the fluid without agglomerating and without obstructing the pipes when the temperature of the transported fluid is not too low.
Reference can be made in this connection to patent application EP-A-323,774 in the name of the present applicant, which describes the use of nonionic amphiphilic compounds chosen from among esters of polyols and carboxylic acids, in substituted or unsubstituted form, and compounds having an imide function. Patent application EP-A-323,775, also in the name of the applicant, describes the use of compounds belonging to the family of diethanol amides of fatty acids or fatty acid derivatives, U.S. Pat. No. 4,856,593 describes the use of surfactants, such as organic phosphonates, phosphate esters, phosphonic acids, their salts and esters, inorganic polyphosphates and their esters, as well as polyacrylamides and polyacrylates. Patent application EP-A-457,375 describes the use of anionic surfactants, such as alkyl aryl sulphonic acids and their alkali metal salts.
These compounds are suitable when the liquid phase is formed from water and liquid hydrocarbons, such as e.g. a condensate or an oil, but are less satisfactory when the liquid phase is constituted in majority or sole manner by water (case of dry gases).